12 December 1989 Stoichiometry Considerations On Optical And Electrochromic Properties Of Sputtered Tungsten Oxide Films
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Tungsten oxide films of varying stoichiometry were deposited by d.c. magnetron sputtering and their optical and electrochromic (EC) properties were investigated. Spectrophotometric transmittance characteristics of the films on Corning 7059 substrates were used to evaluate optical constants and determine absorption spectra of the samples. Films on conductive transparent layers were used to study the EC behavior of the films. Film stoichiometry was deduced from the effective medium model using optical frequency dielectric constants. Oxygen deficiency in W03 leads to an as deposited blue color, the result of a broad absorption band at - 1μm. This broad band has been resolved into three selective absorption bands and an impurity band model is presented as an explanation. It is postulated that lithium insertion/reduction in W03 leads to the same color appearance by creating the same absorption bands and that electrochromic performance in the visible region can be optimized by using a film that is slightly reduced as deposited. In this case the impurity bands are already established and less lithium reduction is required to cause a visible change. It is found that electrochromic performance is optimized in films of stoichiometry around WO2.97 and that as deposited films reduced beyond WO2.86 are not electro-chromic.
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H. Demiryont, H. Demiryont, S. C. Schulz, S. C. Schulz, "Stoichiometry Considerations On Optical And Electrochromic Properties Of Sputtered Tungsten Oxide Films", Proc. SPIE 1149, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion VIII, (12 December 1989); doi: 10.1117/12.962164; https://doi.org/10.1117/12.962164


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